Flumioxazin, a PPO inhibitor: A weight-of-evidence consideration of its mode of action as a developmental toxicant in the rat and its relevance to humans.

Flumioxazin, is a herbicide that has inhibitory activity on protoporphyrinogen oxidase (PPO), a key enzyme in the biosynthetic pathway for heme. Flumioxazin induces anemia and developmental toxicity in rats, including ventricular septal defect and embryofetal death. Studies to elucidate the mode of action (MOA) of flumioxazin as a developmental toxicant and to evaluate its relevance to humans have been undertaken. The MOA in the rat has now been elucidated. The first key event is PPO inhibition, which results in reduced heme synthesis in embryonic erythroblasts. The critical window for this effect is gestational day 12 when almost all erythroblasts are at the polychromatophilic stage, synthesizing heme very actively. Embryonic anemia/hypoxemia is induced and the heart pumps more strongly as a compensatory action during organogenesis, leading to thinning of the ventricular walls and failure of the interventricular septum to build completely and close. Investigations showed that this MOA is specific to rats and has no relevancy to humans. Flumioxazin inhibited PPO in rat hepatocyte mitochondria more strongly than in human. A 3-dimensional molecular simulation revealed that species differences in binding affinity of flumioxazin to PPO, observed previously in vitro, were due to differences in binding free energy. In vitro studies using several types of rat and human cells (erythroblasts derived from erythroleukemia cell lines, cord blood, or pluripotent stem cells), showed that flumioxazin decreased heme synthesis in rat cells but not in human cells, demonstrating a clear, qualitative species difference. Considering all available information, including data from PBPK modelling in rat and human, as well as the fact that anemia is not a symptom in patients with variegate porphyria, a congenital hereditary PPO defect, shows that the sequence of events leading to adverse effects in the rat embryo and fetus are very unlikely to occur in humans.

Historical control data on developmental toxicity studies in rodents.

Historical control data on rodent developmental toxicity studies, performed between 1994 and 2010, were obtained from 19 laboratories in Japan, including 10 pharmaceutical and chemical companies and nine contract research organizations. Rats, mice, and hamsters were used for developmental toxicity studies. Data included maternal reproductive findings at terminal cesarean sections and fetal findings including the spontaneous incidences of external, visceral, and skeletal anomalies. No noticeable differences were observed in maternal reproductive data between laboratories. Inter-laboratory variations in the incidences of fetuses with anomalies appeared to be due to differences in the selection of observation parameters, observation criteria, classification of the findings, and terminology of fetal alterations. Historical control data are useful for the appropriate interpretation of experimental results and evaluation of the effects of chemical on reproductive and developmental toxicities.

Historical control data on prenatal developmental toxicity studies in rabbits.

Historical control data on rabbit prenatal developmental toxicity studies, performed between 1994-2010, were obtained from 20 laboratories, including 11 pharmaceutical and chemical companies and nine contract laboratories, in Japan. In this paper, data were incorporated from a laboratory if the information was based on 10 studies or more. Japanese White rabbits and New Zealand White rabbits were used for prenatal developmental toxicity studies. The data included maternal reproductive findings at terminal cesarean sections and fetal findings including spontaneous incidences of morphological alterations. No noticeable differences between strains or laboratories were observed in the maternal reproductive and fetal developmental data. The inter-laboratory variations in the incidences of fetal external, visceral, and skeletal alterations seem to be due to differences in the selection of observation parameters, observation criteria, and classification of the findings, and terminology of fetal alterations.

Pancreatic endocrine tumor with partial acinar cell differentiation.

We examined a 70-year-old woman in whom a pancreatic endocrine tumor with partial acinar cell differentiation had been diagnosed. She had neither endocrine nor exocrine symptoms. The tumor was located in the pancreatic tail and measured 12.5 x 9.5 x 8 cm. It had a capsule, was composed of multiple adhesion nodules, and was elastically soft, medullary, and yellowish white. The neoplastic cells had large, irregular, oval nuclei; prominent eosinophilic nucleoli; and abundant eosinophilic cytoplasm with many fine granules. The cells had proliferated in islet-like solid medullary, trabecular, acinar, and papillary patterns. Most neoplastic cells were strongly positive for synaptophysin. 10 to 25% of the neoplastic cells were positive for alpha1-antitrypsin. Neuroendocrine and zymogen granules were simultaneously observed in the cytoplasm of the same neoplastic cells at the ultrastructural level. The tumor may be considered an amphicrine tumor.

Pancreatic, hepatic, splenic, and mesenteric mucinous cystic neoplasms (MCN) are lumped together as extra ovarian MCN.

Mucinous cystic neoplasms (MCN) of the pancreas are mucin-producing cystic tumors with an ovarian-like stroma (OLS). In the present study MCN were obtained from 27 patients. These MCN were derived from 22 pancreas, three livers, spleen, and mesentery. MCN in various organs have common clinicopathological profiles, being unilocular or multilocular cystic tumors, with a fibrous capsule and lined by mucin-secreting epithelium associated with an underlying subepithelial OLS. The OLS showed strong positivity for alpha-smooth muscle actin (alpha-SMA) and vimentin and weak, focal positivity for desmin. Both estrogen receptors and progesterone receptors were expressed in the nuclei of OLS cells. In addition, 20 ovarian MCN and 13 normal ovaries were studied with particular attention to the stroma. The stroma of ovarian MCN was strongly immunopositive for alpha-SMA and vimentin and focally positive for desmin, whereas normal ovarian stroma was immunonegative for both alpha-SMA and desmin. The OLS of MCN mentioned here was similar to the septa of ovarian MCN but not to ovarian stroma. In conclusion, MCN in various organs should be lumped together as 'extra ovarian' MCN. The OLS was identified on the basis of myofibroblastic proliferation both in response to neoplastic development and dependent on hormones.

A simple X-ray emitter.

A compact X-ray emission instrument is made, and the X-ray spectra are measured by changing the applied electric potential. Strong soft X-rays are observed when evacuating roughly and applying a high voltage to an insulator settled in this device. The X-ray intensity is higher as the applied voltage is increased. A light-emitting phenomenon is observed when this device emits X-rays. The present X-ray emitter is made of a small cylinder with a radius of 20 mm and a height of 50 mm. This X-ray generator has a potential to be used as an X-ray source in an X-ray fluorescence spectrometer.

Inflammatory response and cathepsins in silica-exposed Hermansky-Pudlak syndrome model pale ear mice.

Hermansky-Pudlak syndrome (HPS) is a hereditary disorder involving the sorting processes of intracellular organelles such as lysosomes of reticuloendothelial cells. Pale ear (ep) mouse is known to have the HPS1 gene mutation, which is seen in patients with HPS and pulmonary fibrosis. As pulmonary fibrosis is not spontaneously observed in ep mice, we hypothesized that external stimuli are necessary for the genetic predisposition of its development. We used silica as the external stimulus to induce the alveolar macrophage-mediated inflammatory response and evaluated the pathological changes of the lung and biochemical analysis of collagenolytic lysosomal enzymes cathepsins L and B in ep mice. Treatment with silica induced the following: persistent accumulation of activated macrophages; delayed clearance of silica from alveolar spaces; and increased collagen fibers in alveolar tissues, which were shown with trichrome staining in ep mice. The comparison of bronchoalveolar lavage cells between the naïve ep and control mice revealed: decreased enzymatic activities but increased antigenic levels of cathepsins L and B, resulting in significantly lower ratios of activity to antigen; increased ceroid deposits and cathepsin L antigens in lysosomes; and no abnormal forms of cathepsins were detected. After silica instillation, activities of cathepsin L in the ep mice increased but ratios of activity to antigen were still significantly low. These phenomena induced by silica suggest that external stimuli bring forth fibrogenesis in the animal models or humans that have HPS1 gene mutation.